#include<bits/stdc++.h>
using namespace std;

class Solution {
public:
    int climbStairs(int n) {
        int dp[n+2];
        memset(dp,0,sizeof dp);
         dp[1] = 1;
         dp[2] = 2;
        for(int i=3;i<=n;i++){
            dp[i] = dp[i-1] + dp[i-2];
        }
        return dp[n];
    }
};